1. Field of the Invention
This invention relates to the atomization of liquids by means of a piezoelectric vibrator and more specifically it concerns novel methods and apparatus for controlling such atomization in an efficient and effective manner.
The present invention also relates to means for the distribution of a liquid active material, such as a perfume, air freshener, insecticide formulation, or other material, in the form of fine particles or droplets, as in a fine spray, by means of a piezoelectric device. In particular, the invention is directed to a piezoelectric liquid delivery system for production of droplets of liquid, or liquid suspensions, by means of an electromechanical or electroacoustical actuator. Even more specifically, the present invention relates to an improved control circuit for use with such devices.
2. Description of the Related Art
The use of piezoelectric vibrators to atomize liquids is well known; and examples of such devices are described in U.S. Pat. No. 5,164,740, U.S. Pat. No. 4,632,311 and U.S. Pat. No. 4,533,082. In general, these devices apply an alternating voltage to a piezoelectric element to cause it to expand and contract. The piezoelectric element is coupled to a perforated orifice plate, which in turn is in contact with a liquid source. The expansion and contraction of the piezoelectric element causes the orifice plate to vibrate up and down whereupon liquid is driven through the orifice plate's perforations and is then thrown upwardly in the form of fine aerosolized particles.
It is desired to provide a battery driven piezoelectric atomizer which operates over a long period of time without deterioration of its performance and which permits the use of inexpensive alkaline batteries whose voltage output is known to decrease over the operating life of the battery.
One way in which a piezoelectric atomizer can be driven economically is to control it to operate during drive periods which are separated by sleep periods, so that liquid becomes atomized during the drive periods in successive short puffs. However, during the sleep periods between puffs, liquid accumulates on the orifice plate; and in order to start a successive puff at the next drive period, the orifice plate must be driven at a large amplitude.
Another way in which a battery operated piezoelectric atomizer can be operated economically is to drive it at the resonant frequency of its vibrating system, which includes the orifice plate, the piezoelectric element and any mechanical coupling between the orifice plate and the element. A problem occurs, however, because the resonant frequency may vary somewhat from device to device so that a different driving frequency must be set for each unit.
The distribution of liquids by formation of a fine spray, or atomization, is well known. One method for such distribution is to atomize a liquid by means of the acoustic vibration generated by an ultrasonic piezoelectric vibrator. An example of such a method is shown in U.S. Pat. No. 4,702,418, which discloses an aerosol dispenser including a nozzle chamber for holding fluid to be dispensed and a diaphragm forming at least a portion of the chamber. An aerosol dispensing nozzle is disposed therein, with a restrictive passage for introducing liquid from the reservoir to the nozzle. A pulse generator in combination with a low voltage power source is used to drive a piezoelectric bender, which drives fluid from the reservoir through the nozzle to create an aerosol spray.
Another atomizer spraying device is shown in U.S. Pat. No. 5,518,179, which teaches a, liquid droplet production apparatus comprising an orifice plate which is vibrated by an actuator which has a composite thin-walled structure, and is arranged to operate in a bending mode. Liquid is supplied directly to a surface of the orifice plate and sprayed therefrom in fine droplets upon vibration of the orifice plate.
U.S. Pat. Nos. 5,297,734 and 5,657,926 teach ultrasonic atomizing devices comprising piezoelectric vibrators with a vibrating plate connected thereto.
In U.S. Pat. No. 5,297,734, the vibrating plate is described as having a large number of minute holes therein for passage of the liquid.
While a number of additional patents disclose means for the dispersion of liquids by ultrasonic atomization, or for timed intervals of dispersion, they have achieved only moderate success in the efficient atomization of such materials as perfumes. See, e.g., U.S. Pat. Nos. 3,543,122, 3,615,041, 4,479,609, 4,533,082, and 4,790,479. The disclosures of these patents, and of all other publications referred to herein, are incorporated by reference as if fully set forth herein.
Such atomizers fail to provide an easily portable, battery operated dispenser employing an orifice plate in mechanical connection with a piezoelectric element, capable of long periods of use with little or no variation in the delivery rate. Furthermore, the efficiency of these atomizers may differ due to manufacturing differences in the atomizer piezoelectric pump components. Thus, a need exists for improved atomizers or dispensers for use in distribution of active fluids such as fragrances and insecticides, which atomizers are highly efficient and consume minimal electrical power while providing wide dispersal of the liquid.